chore(backend): refactor config and startup

[ivanskv2000]

chore(backend): refactor environment configuration and server startup

✨ What’s Changed?

• Infrastructure Enforcement: Added model_validator to ensure DATABASE_URL is provided at runtime, while maintaining Pylance compatibility with field defaults.
• Security Enhancements:
  • Added a masked_database_url property to Settings to prevent credential leakage in logs or public endpoints.
  • Updated /config endpoint to use the masked URL.
• Improved Server Lifecycle:
  • Introduced structured Python logging in main.py controlled by environment-specific log levels.
  • Enhanced the lifespan context manager in factory.py for graceful database connection disposal.
  • Refactored create_app factory to accept the database engine instance.
• Auth Refactoring: Decentralized settings in auth modules by using get_settings() inside functions, improving testability and preventing import-time instantiation issues.
• Test Alignment: Updated the test suite and conftest.py to correctly handle the new configuration patterns and ensure .env.test is prioritized.
• CI Adjustment: Added a step to the GitHub Actions workflow to dynamically generate a CI-specific .env.test, ensuring connect to the CI Postgres service.

📂 Scope

• frontend
• backend
• common/shared
• CI/config

📝 Notes (Optional)

This refactor transforms the previous configuration "plumbing" into a reliable, multi-environment system that strictly enforces required infrastructure while respecting local overrides.

✅ Checklist

• PR title uses Conventional Commit format
• Code is clean and commented where needed
• I’ve manually tested relevant parts
• I’ve updated docs (if needed)

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud